A benzyl (Bn) group and substitution products thereof have been utilized as protecting groups in the field of organic synthetic chemistry for a long time (for example, see Non Patent Literature 1). The biggest advantage of Bn-based protecting groups is that they can be easily and cleanly removed by hydrogenolysis (for example, H2 and Pd/C). Especially a p-methoxybenzyl (PMB) group and a 2-naphthylmethyl (NAP) group can be easily removed with an oxidant such as dichlorodicyanobenzoquinone (DDQ) or ammonium cerium nitrate (CAN) and therefore are excellent in that they can be removed separately from a Bn group (for example, see Non Patent Literature 1).
While removal is easy, strongly basic (for example, NaH, BnBr, and DMF, or DIPEA, BnBr, neat, and 150° C. (for example, see Non Patent Literature 2)) or strongly acidic (for example, BnOC(NH)CCl3 and TfOH) (for example, see Non Patent Literature 3) conditions are usually needed for the introduction of a Bn-based protecting group (a large number of examples using Lewis acids are also known)T. These conventional methods are also problematic in that they are hard to be applied to a small scale experiment and to be conducted by a person who are not trained as a synthetic organic chemist, because all of these reactions are moisture-sensitive. For protecting an alcohol unstable to acids and bases, benzyloxymethyl (BOM) groups, which can be introduced in the presence of a weaker base, diisopropylethylamine (DIPEA) are generally utilized. So far, as an oxidatively removable protecting group in the later stage of multistep synthesis, a p-methoxybenzyloxymethyl (PMBOM) group has been used (for example, see Non Patent Literature 1).